In a process of manufacturing a semiconductor device, a tungsten (W) film is used to fill up recesses (via holes) between wirings or recesses (contact holes) for substrate contact.
As a film forming method of the tungsten (W) film, physical vapor deposition (PVD) has been used in the past. However, since tungsten is metal with a high melting point and it is difficult to cope with high coverage due to the recent miniaturization of devices in the PVD, chemical vapor deposition (CVD) which can sufficiently cope with high coverage and miniaturization of devices is being mainly used.
When filling the W film in the via holes or contact holes by CVD, from the viewpoint of reaction suppression or the adhesion with a silicon layer, a TiN film is formed as a barrier layer on the silicon layer, and the tungsten film is deposited thereon.
During deposition of the tungsten film, the deposition is mainly performed by the reaction of WF6+3H2→W+6HF using tungsten hexafluoride (WF6) as a raw material of tungsten, and a H2 gas as a reducing gas. However, in the first nucleation, a SiH4 gas or B2H6 gas having a reducing power greater than H2 gas is used as a reducing gas (see, e.g., Japanese Patent Application Publication Nos. 2003-193233 and 2004-273764).
However, since silicon (Si) atoms or boron (B) atoms are incorporated into the tungsten film in the case of performing the nucleation of tungsten by using SiH4 gas or B2H6 gas as a reducing gas, the resistance is high compared to a pure tungsten film. Due to the recent miniaturization of contact holes, the W film having a lower resistance is required, and the nucleation using SiH4 gas or B2H6 gas no longer meets the requirements. Further, in the case of using B2H6 gas as a reducing gas, it is possible to lower the resistance than when using SiH4 gas, but electrical characteristics may be deteriorated or the adhesion with the underlying film may be deteriorated due to diffusion of B.